The temperature rise from the operation of implanted biomedical devices should be kept within a safe limit to prevent thermal damage or any undesirable thermal effects. To evaluate the temperature rise from the operation of an implanted high-density microelectrodes array (MEA) on a flex in the subretinal space, we directly integrated resistance temperature detectors into this retinal MEA device in the same micro fabrication. We surgically implanted this MEA device in the subretinal space of a rabbit model and measured the temperature rise in vivo. The measured temperature rise is consistent with the calculated values from the finite element method. Experiment showed the temperature versus power dissipation of the MEA device had a slope of . To ensure the temperature rise is within 1.0°C, the maximum power dissipation on the retinal implant should be kept within .